There are, of course, many patents which relate to the treatment of biochemical waste and to processes for anaerobic digestion of biochemical waste materials. Efforts have, in fact, centered upon elimination of the extent of pollution created by these systems, and to methods for enhancing these anaerobic treatment systems to increase their overall efficiency. For example, in Ishida et al., U.S. Pat. No. 4,067,801, there is disclosed a two-stage anaerobic treatment system in which a solid separation step is provided between a first acidogenic stage and a second methanogenic stage, with the solids being recycled to the acidogenic reactor. Solids from the methanogenic reactor are then separated from the effluent and a portion is returned to the methanogenic reactor, with the remainder disposed of as a waste stream. Similarly, in Srivastava, U.S. Pat. No. 5,500,123, another two-stage anaerobic digestion system is disclosed, which includes partial recycle of solids from the methanogenic stage to the acidogenic stage.
Furthermore, in Kubler, U.S. Pat. No. 5,529,692, yet another two-phase anaerobic treatment is disclosed in which biosolids are recycled and are conditioned prior to being added to the methanogenic reactor. As is disclosed in Kubler, this conditioning is a biological hydrolysis step requiring pH control within a critical range, and solids retention times on the order of three days. The conditioning step in Kubler is said to promote methane generation in a second phase of the anaerobic reactor.
In other patents, there has been a general recognition that electrolysis is a method for reducing the organic content of waste streams per se. Thus, for example, in Ghosh et al., U.S. Pat. No. 4,696,746, the acidogenic effluent from a two-stage anaerobic reactor system is divided into two steams for treatment in separate methanogenic reactors. One of these streams is enriched in molecular hydrogen to promote the generation of methane and to minimize carbon dioxide evolution. Thus, the object of this process is to increase the overall generation of methane by the anaerobic treatment process, and the patentees disclose recycle of biosolids into the reactor system for use of an electrolytic process to facilitate digestion of biosolids generated by the anaerobic stages. Similarly, in Dietrich, U.S. Pat. No. 5,364,509, black water and gray water sewage are treated in electrolytic cells. This electrolysis is said to be sufficient to reduce the biological oxygen demand (BOD) and total suspended solids (TSS) of the waste water to levels suitable for surface water discharge. The process disclosed in this patent uses an electrolysis cell as the sole treatment unit and does not discuss integration of electrolysis into a more comprehensive treatment system.
In Roychowdhury, U.S. Pat. No. 6,090,266, processes are disclosed for producing hydrogen from anaerobic decomposed organic materials. These organic materials are thus subjected to anaerobic decomposition under acidogenic conditions and then treated with an anaerobic reactor comprising an electrolytic cell. After current application in the cell, methane generation is suppressed and hydrogen production increased. Thus, upon termination of the electric current, methane generation resumes.
In other patents, the use of electrolysis to facilitate biodegradation of certain cellulosic materials is also disclosed, such as in Eskamani et al., U.S. Pat. No. 4,341,609, and Magnier et al., U.S. Pat. No. 695,573, which disclose electrolysis used to facilitate biological conversion of plant biomass.
Furthermore, in my own prior U.S. Pat. No. 5,492,624, which is an improvement over my prior U.S. Pat. Nos. 4,915,840 and 5,141,646, I disclose a process for treating organic waste by feeding the waste to an autothermal aerobic digestion unit where it is subjected to biological digestion, and in which at least a portion of the biomass produced therein is oxidized, preferably by chemical oxidation step, such as using hydrogen peroxide in the presence of a centens reagent catalyst, such as ferrous sulphate, and then returning the oxidized effluent to the autothermal aerobic digestion unit itself.
Efforts have continued, however, to improve on all of these processes and to further reduce the generation of unwarranted pollutants from said biological processes.